Such a method and an associated apparatus are known from U.S. Pat. No. 4,827,937. The apparatus has a precontrol means, a desired-value generator means, a control means and an adaptation factor memory. The process serves, for example, for adjusting the injection time. The precontrol means outputs a precontrol value for the injection time dependent upon values of other operating variables than the injection time. The desired-value generator means supplies a single controlled variable desired value, namely the lambda value 1. This value is compared with the respective lambda actual value, which is measured by a lambda probe. The control means forms a control output, namely a control factor, dependent upon the difference between the two values and the respective precontrol value is corrected with the control factor in a closed-loop manner by multiplication. However, the precontrol value is also corrected under open-loop control, that is with the aid of an adaptation factor read out from the adaptation factor memory. The adaptation factor memory stores adaptation values which are addressable via values of addressing operating variables. For correcting the precontrol value, the memory reads out the adaptation factor which belongs to the set of values of the addressing operating variables existing in that particular case. The precontrol value is multiplicatively combined with this factor. The adaptation factors are always redetermined with the aid of the control factor supplied by the control means. At predetermined longer time intervals, the factors of the adaptation factor memory are evaluated to the extent that the average value of all the factors is formed and this average value is incorporated in a so-called multiplicative global factor. This value then globally takes into account corrections which are necessary both due to disturbing influences acting multiplicatively on the injection time as well as disturbing influences acting additively.
Additively acting disturbing influences are better taken into account in a method such as that known from SAE paper number 860594, 1986, likewise for adjusting the injection time. Apart from the above-mentioned function stages, the associated apparatus also has a summand-determining means, which determines a summand which is added to the precontrol value corrected by multiplicative factors. The summand is measured in idling, that is with small injection times. This is due to the consideration that, with small injection times, a multiplicatively acting disturbing influence has a relatively weak effect, but an additively acting disturbing influence has a relatively strong effect.
The system just mentioned has the following disadvantage. The case may readily occur where, even with small injection times, an additively acting disturbing influence compensates itself with an opposing multiplicatively acting disturbing influence. Then, the precontrolled time is not corrected additively (and opposingly multiplicatively), although this actually would be necessary. This error, which originates from the determination in idling, has an effect in the entire load and speed range of the internal combustion engine.
The invention is based on the object of specifying a method for learning control with precontrol for adjusting the lambda value which takes better into account disturbing influences which act additively on the metering of the quantity of fuel than known methods. The invention is also based on the object of specifying an apparatus for carrying out such a method.